The present invention relates generally to communication networks, and more specifically, to a method and system for supporting a GMPLS (Generalized MultiProtocol Label Switching) hierarchy through multiple routing instances.
The rapid growth of the Internet and the widespread deployment of networks built around the Internet Protocol suite are creating a demand for new capabilities in IP (Internet Protocol) networks. MultiProtocol Label Switching (MPLS) provides a number of powerful capabilities such as traffic engineering, etc. As with IP routers, MPLS nodes use a routing protocol such as OSPF or IS-IS to calculate network paths and establish reachability. MPLS is an IETF (Internet Engineering Task Force) initiative that integrates Layer 2 information about network links (bandwidth, latency, utilization) into Layer 3 (IP) within a particular autonomous system in order to simplify and improve IP packet exchange. MPLS provides network operators a great deal of flexibility to divert and route traffic around link failures, congestion, and bottlenecks.
MPLS enabled networks are becoming increasingly important for today's service providers (SPs) in the design and deployment of current and future networks. A primary contributing factor is that MPLS, as an enabling technology, has the capability of converging not only voice, data, and video, but also frame, cell, and packet networks into a single network. Deploying and managing a single and scaleable network is a great benefit to service providers. Furthermore, MPLS networks also allow service providers to do traffic engineering, and quickly reroute customer traffic upon identification of a link failure within their network. This is an important feature for carrier class networks.
Generalized MPLS (GMPLS) extends MPLS to provide a control plane (signaling and routing) for devices that switch in domains such as packet, time, wavelength, and fiber. This common control plane simplifies network operation and management by automating end-to-end provisioning of connections, managing network resources, and providing a level of QoS that is expected in new applications. GMPLS extends the suite of IP-based protocols that manage and control the establishment and release of label switched paths (LSPs) that traverse any combination of packet, TDM, and optical networks.
The IETF work on GMPLS defines support for using the MPLS Traffic Engineering routing and signaling mechanisms to set up connections across networks which use a variety of switching mechanisms. The IETF also describes a hierarchy of different network types and the concept of a device which sits at the boundary of a hierarchy region (see, Internet Draft “LSP Hierarchy with Generalized MPLS TE”, draft-ietf-mpls-lsp-hierarchy-08.txt, Kompella et al., March 2002). For example, a router connected to an optical switch would provide the boundary between the frame and optical regions of a network.
However, the Internet Draft does not define how to integrate two such regions. The Internet Draft implies that both regions of the network would participate in a single instance of routing and signaling. From a practical point of view, it may not be possible to deploy such a network. For example, an Internet Service Provider (ISP) operator may want to deploy GMPLS into a network made up of routers which may or may not be running MPLS. The existing network may have a defined organization of its routing domain (Interior Routing Protocol or IGP (Interior Gateway Protocol) domain). In particular, the ISP may have divided the network into areas as defined by the OSPF protocol specification, or “levels” as defined by IS-IS. Current implementations of MPLS traffic engineering support a single area or level. Routers which need to see the full topology of the network in order to calculate the optimum path for an LSP must be in the same area. IGPs typically require that such areas or levels be contiguous, and define a single backbone area (e.g., “area 0” for OSPF).
The ISP operator may not want to merge the IGP of an experimental optical region with that of the existing frame network. The two networks may be running two different IGPs. The existing frame network may use, for example, ISIS, but the optical switch devices may only support OSPF. The ISP may not want to risk destabilizing the existing IGP by introducing a new implementation into the network. Furthermore, deploying the optical region as, for example, OSPF area 0, would require reconfiguring the existing IGP, which is not very practical.
The ISP operator may also be concerned about leaking addressing information from the optical region into the frame region. Since optical switches cannot, in general, provide connectionless packet forwarding, such leakage may cause forwarding problems in cases where LSPs have not been established between two edge routers.
There is, therefore, a need for a method and system which allow deployment of GMPLS into an existing network without disrupting the existing IGP.